An organic LED element is one in which an organic layer is put between electrodes, and a voltage is applied between the electrodes to inject holes and electrons, which are be recombined in the organic layer, thereby extracting light that a light-emitting molecule emits in the course of transition from an excited state to a ground state.
Generally, light generated in the organic layer is transmitted to an electrode and reaches an interface between the electrode and a glass substrate. However, since the difference in the refractive index is large between the electrode and the glass substrate, a phenomenon occurs in which the light passing through the electrode is reflected at the glass substrate, and then returns to the electrode and the organic layer again. Accordingly, the amount of the light which can be extracted to the outside of the organic LED element is less than 20% of the emitted light in the present circumstances.
Accordingly, there is a document which proposes that a light scattering layer is provided on one surface of a substrate to improve the light-extraction efficiency (Patent Document 1).
Also, there is a document which proposes that an electrode is provided between a glass substrate and a glass layer (Patent Document 2).